"act or state of being or appearing to grow young again," 1834, noun of action from rejuvenate.
c. 1300, from French Turc, from Medieval Latin Turcus, from Byzantine Greek Tourkos, Persian turk, a national name, of unknown origin. Said to mean "strength" in Turkish. Compare Chinese tu-kin, recorded from c. 177 B.C.E. as the name of a people living south of the Altai Mountains (identified by some with the Huns). In Persian, turk, in addition to the national name, also could mean "a beautiful youth," "a barbarian," "a robber."
In English, the Ottoman sultan was the Grand Turk (late 15c.), and the Turk was used collectively for the Turkish people or for Ottoman power (late 15c.). From 14c. and especially 16c.-18c. Turk could mean "a Muslim," reflecting the Turkish political power's status in the Western mind as the Muslim nation par excellence. Hence Turkery "Islam" (1580s); turn Turk "convert to Islam."
Meaning "person of Irish descent" is first recorded 1914 in U.S., apparently originating among Irish-Americans; of unknown origin (Irish torc "boar, hog" has been suggested). Young Turk (1908) was a member of an early 20c. political group in the Ottoman Empire that sought rejuvenation of the Turkish nation. Turkish bath is attested from 1640s; Turkish delight from 1877.